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74. Effect of Phytate and Chitosan on the Accelerating Removal of 65Zn in Rats
Yoshikazu Nishimura, An Yan*, Hee Sun Kim**, Yoshito Watanabe and Masae Yukawa
(*China Institute for Radiation Protection; **STA Fellow)
Keywords: Zn-65, Chitosan, Phytate, Biokinetics
Radioactive zinc is produced by neutron activation and is sometimes contained in reactor coolant. It is known that naturally occurring phytate found in plant protein can reduce the availability of dietary zinc. Several investigators have confirmed that phytate forms an insoluble calcium-zinc-phytate complex in the intestinal lumen and reduces the reabsorption of endogenous zinc secreted into the intestinal tract. Chitosan is derived from chitin, which is a cellulose-like biopolymer distributed widely in nature, especially in crustaceans, insects, fungi and yeast. It is a natural chelating agent. The purpose of the present study was to investigate whether phytate and chitosan can be applied to animal and human bodies in order to reduce the bioavailability of radio-zinc.
Wistar strain male rats, 8 weeks of age, were used in this experiment. Four groups of rats were given the following dietary treatments: (1) Normal diet (Oriental Yeast Co., Tokyo) and 3 % phytate water, (2) Cubed diet containing 5% of chitosan and distilled water, (3) Cubed diet containing 5% of chitosan and 1 % phytate water, (4) Normal diet and distilled water. Each group consisted of five rats, and they were kept for about 1 week under these conditions. After that, 65Zn chloride was administered orally using a stomach tube. Whole-body retention was then measured. To determine the initial dose of radio-zinc in each animal, whole-body measurements of 65Zn were made immediately after administration and were followed periodically thereafter by in vivo counting with a small animal counter (Armac Model-446, Packard Instrument Co.). Fig. 24 shows the whole-body retention of 65Zn in the rats after oral administration. The whole-body retention of 65Zn decreased sharply in the rats given 3 % phytate water in advance of 65Zn administration when compared with the control rats. The rats given 5% chitosan and 1 % phytate water also showed a significant reduction in radio-zinc. However 5 % chitosan did not have a significant effect on accelerating the removal of radio-zinc in rats. Previous studies have shown that 1% phytate is also not effective in reducing radio-zinc in rats. These results suggest that the effectiveness of phytate and chitosan in reducing the bioavailability of radio-zinc depends on the concentration of phytate and chitosan.
